With the independent discovery by Girardot et al. (1974) and by Stenflo et al. (1974) that the vitamin K dependent step in the finalization of prothrombin is the carboxylation of glutamyl residues on a preformed precursor protein, this application is concerned with the elucidation of this reaction and the characterization of its components. The proposed research will involve the isolation and purification of the vitamin K dependent carboxylation enzyme, the characterization of the functional form of vitamin K and the study of the mechanism for the activation and transfer of the CO2 molecule.